This invention relates to a new all season tire tread rubber comprising low vinyl polybutadiene, polyisoprene, and a diene polymer having a glass transition temperature of about -5.degree. to about -20.degree. C.
Tire tread compositions are engineered to produce traction, speed, stability, and casing protection, simultaneously providing frictional contact for the transmission of driving, braking and cornering forces as well as wear resistance. Typical tread rubber compositions employ elastomers having a relatively high tensile strength and high abrasion resistance. However, compounding elastomers for improved traction may adversely affect abrasion resistance and tire rolling resistance; conversely, tire traction can suffer when trying to improve rolling resistance. To balance these counteracting considerations, blends of styrene/butadiene and butadiene rubber are commonly employed in passenger tires (Bhakuni, et al., Encyclopedia of Polymer Science and Engineering, 2nd ed., volume 16, John Wiley, 1989, page 838); other elastomers such as natural rubber may be used to modulate cure, dynamic, or physical properties, or the flex fatigue life of the tire. Fillers, notably carbon black, are added to reinforce the elastomers and improve strength (Eirich, F., Science and Technology of Rubber, Academic Press, New York, 1978, pages 374 and 375 and Bhakuni, et al., cited above, page 842).
For example, Studebaker and Beatty described three tread compositions: two had styrene/butadiene elastomers and one had natural rubber (Eirich, F.R., Science and Technology of Rubber, Academic Press, 1978, pages 374 to 375; compounds 188, 208 and 211 are treads). Bridgestone disclosed a tire rubber composition comprising 50 to 85 parts by weight of natural rubber or synthetic polyisoprene, 5 to 20 parts by weight of high styrene styrene/butadiene, and 5 to 45 parts by weight of low styrene styrene/butadiene (Jap. Pat. Ap. Pub. No. 2,129,240). Takino, et al., disclosed a tire tread rubber composition having a two-peak loss tangent curve and comprising isoprene containing more than 50% total 3,4- and 1,2-vinyl bonds and styrene/butadiene in a ratio of 5/95 to 60/40, with 50 to 200 parts by weight carbon black (U.S. Pat. No. 4,946,887).